Desires are often taken to be the basis for all practical reasons. I introduce one of the most powerful arguments to sustain this view: the argument from motivation (sec. 1). In section 2, however, I develop an equally powerful objection to desire-based approaches showing that desires are not suited to accommodate the justificatory role of reasons. The objection suggests that at least one of the premises of the argument from motivation must presuppose that only desires can explain actions. This move is, however, fatal for desire-based views of practical reason.